Maximum kilovoltage limiter for x-ray tubes



3 Feb. 6, 1945. J. BALL 2,368,798

MAXIMUM KILOVOLTAGE LIMITER FOR X-RAY TUBES 7 Filed Aug. 15, 1942 INVENTOR g4 JACK BALL V "xeray tube "at various *kilovoltages is included Patented Feb. 6, 1945 um smras PAT ENT o- FICE .ZMAXIMUMiKILOVOLTAGE L IMIT v X- RAY TUBES ERIFOR i JacliiBall, Euclid, "Ohio, assignor to Picker X-Jtay Corporation "iWaite "Manufacturing iDivision, IncJClevelarid; Ohio, a corporation of Ohio A pplicationAugust15, 1942; SeriaI-No. 454,926

17 Claims. (Cl. 250103) one embodiment ZlSShOWIlf'iIlEthG-Y accompanying drawing vmarked ,F'ig. 1" and;.-'it"willl :be rounder- '-stood by those skilled; in ithesart .how lthe same principle .maybe *appliedJ-in various ways.

It will be understood why those skilled: this :"art 1 that it is desirable :to f.-1imit :the ,maximum kilovoltage (used .=at ,wany "given i tube load wwhen :makingan'exposure. -To-exceed :this desirable kilovoltage Y may damage the tube *orlin .any i case shorten its life. :The purpose of :the present invention, therefore, is to provides-an automatic 1 control making it impossiblenfor the operator .to exceed a predetenninedki-lovoltagewhen: the lapparatus has been set for a fixed load. 7 a n In the accompanying-diagrammatic drawing an .X-ray tube at Illis. suppliedvwithuhighftension .current .through the transformer ll havingta iprimary Haand a: secondary lb. The primary is supplied. with current through linesl2 and I3 by meanszof dial selector switchesr=l2atand13a. These engage variousecontactsmconnected with the autotransfor-mer I41 whicheinrturn receives a current .supplye'from ..the .lines L1,. .L2. This, .is a simple circuit usingeonlylhalfewave rectification but it will" be understood.byithose skilledin.the art that thisiis fon.illustrative,purposes only-rand that my. device is applicable to any/type. of .cir-

cuit. Current 'for the. tube filament is supplied from the taps l5 and '16 of the autotrans'former to'the primary 11a of'the filament-transformer I1. I Means'is provided ior'varyingfthejfilament current for various tube" loads. lIn the present *inStance this takes'the form "of: a series of .resist- "ances-l8 connectedyvithtaps l9..on deck'jA of a'selector switchof thermonitor; type.

"A known meansl'forchanging" the indication of "currentsuppliewtothe tube'filamentto. compensate for changes "in "the'" saturation 56f the inthediagramof Fig. 1. 'Thisiszsimilar to.that described and I claimed in" Patent "No. 223L622, granted February 1 1, 19413 EdwardiB. "Graves, to'which further referencemaybehadif "neces- "saryto .understandthisportlon or theJdiagram.

s My invention may beuusedwin-various waysbut of resistances 32 l which are connectedi-with' taps 22 on the deck :B of=-a monitor selector-switch The voltmeter: 23:is incircuit between the points ":24 and-25 sovasrtorreadethe current-flowing in the-filament-circuit. The resistances 2b are thus placed in the: meteringucircuitinseries, with the .compensati-ng coil-20band varyltheindication of i the voltmeter to apply a'correctionto compensate --for changes in tubeoutputdue-torchanges inthe .hightension voltagesupplied to the -transformer ll.

21 and resistor '2 8 are? fully describedw in theabove mentioned patent. g l i ;The--present-invention adds to the known-scircuits above described a control.- circuit. for breaking: the energizing :circuit-through lines 1 2t-and 13 if thepredetermined peakkilovoltagedsexceeded. 1T0 this end-adisconnectorswitch r29 is provided in linel 3- which is held closed by. relay 30 :so long vas the latter is energized. eThe telectricity for the relay i3llisxprovide'd through lines L3, L4 fr0m\ any=.110 -volt source. 'A timer orex- :posure switch is indicated v at 3|. :In.the.relay 1 '-circuit is. provideda normally .closed switch 3 2 which I is: opened by relay, 33 1 whenever the latter isenergized. The present invention -provides for the energization. of thistrela r33 ittoo highia kilovoltage is applied toflthe tube. For thispurpose the controlmcircuit. is supplied with current which variesvinestep withithe currentin lines 1.2 "and. I3 =infthe ,prim ,rytof.thetransformer H. For this purposelines "34 ant-1,535 are v connected with lines l2 and I3 toitheprimary 36a of ,the transformer 36. The secondary36b ofthis transformer is connected to.a rectifier 31 an'dQfilter '38 toisupply rectified current to the controlcircuit. It will be noted thatlthe line 3 5v iscbnjnected to line l3"aheadoftheqswitch 29 so as to provide a steady Voltage to the controlucircuit. "This control circuit is normally nonconducting and is under the controlpofj aithyratrontube39, 'the grid 39bo'f which*is'suppliedjywith'afixed voltage as will later-be described. Whether the tube "iscon'ducting-or nonconducting will then depend'uponithe circuit connected with the plate 39a of the tube. This plate is 'connected' byllinfe 40 to relay 33 Whichinftmn. isconnected by line 4| 'tOBQSBIGCCOI SWitCh on deckC ofithe monitor switch. The 'resistor"42 is "connected withjthe taps '43 on the"'deck'C. 'obviously'the greater the resistance placed in series along the resistor 42 "the "greater must be "the "current. supplied through transformer '36 to-supp1y suflicient voltage 'toplate" 39a."'to"overcomeithe grid bias Jon the grid 39?; "andto cause the thyratron to be;

Thepurposes 1 of the inductor '26, capacitor come conducting. The grid 39b of the thyratron tube is biased by means of transformer 44 and the rectifier and filter circuit 45, 46. The resistor 41 in this circuit is adapted so as to be able to adjust the grid bias for individual tubes and characteristics. The primary of transformer 44 is connected to a stabilized 110 volt source. The transformer 44 is supplied with a secondary 440 for providing current for the filaments of tubes 31, 39 and 45 in the well understood manner.

The operation of the circuitsthus far described is as follows: Th main switch is closed to energize the autotransformer l4. The desired tube load is selected by rotating the monitor switch which has a number of decks, only three of which are shown and all of which are connected together by a shaft 48 which is here diagrammatically represented. The deck A may be calibrated in terms of tube output. At the same time the deck B adjusts the calibration of the voltmeter 23 sothat it is only necessary to adjust the dial switches l2a and l3a until the voltmeter hand registers with the single indication shown. At

the same time that this is done the deck C of the monitor switch is selecting a suitable resistance on the resistor 42'so as to limit the kilovoltage which may safely be applied to the tube At this time the-grid 39b is supplied with a biasing current of such value that the thyratron tube 39 is nonconducting. Switch 32 is therefore in its normally closed position. Exposure switch 3| is then closed, energizing relay 39 to close switch 29 and provide an X-ray tube exposure. If the current across the lines l2 and I3 is of be depended upon to give absolute protection for the tube.

, grid and plate of the tube 39 and it is immaterial which of these is held constant while the other is varied. It is also well understood that a thyra- 'tron or trigger tube like that shown at 39 ,may

such an order as to provide too high a peak kilo- 7 (this being a normally open switch).

Since rectified current is applied to plate 3911,.

once the thyratron tube is rendered conducting it will stay that way until the voltage to transformer 36 is interrupted and lowered below the tripping value of tube 39. This occurs automatically when the dial switches |2a and I311 are moved to lower the peak kilovoltage because between the taps switches l2a, and 13a are nonconducting' and this interrupts the current flow to'transformer 36. Upon such" interruption the grid 39b again resumes control of tube 39 ready for the next operation.

It will be seen that the tripping voltage of tube 39 depends upon the current supplied to the plate 39a and this in .turn is, varied by changing the taps on resistor 42 .by means of the switch on deck C. Thus each position of this switch on deck C corresponds to a maximum voltage which can be applied to the tube I0 and to the transformer 36 of the control circuit before the thyratron tube will become conducting and trip the relay. 7 I

The control apparatus here. disclosed is very positive in action and will trip on one minor selector dial movement over the tripping value set and the setting is very consistent and may be utilized in circuits either normally conducting or normally nonconducting. It will also be understood by those skilled in this art that the flow controlling element, indicated at 42 as a resistor might in some other controlling circuit be an inductor or a capacitor.

What I claim is: I 1. In combination with an X-ray tube and energizing circuit therefor, a control circuit, means responsive to a predetermined condition of said control circuit for disconnecting said energizing circuit, means supplying current to said control circuit varying in accordance with current variations in said energizing circuit, and a control device in said control circuit responsiveto said current supplying means and arranged to produce said predetermined condition of said control circuit in response to current in said energizin circuit above a predetermined level. 2. In combination with an X-ray tube and energizing circuit therefor, a control circuit, means responsive to a predetermined condition of said control circuit for disconnecting said energizing circuit, means supplying current to said control circuit varying in accordance with current variations in said energizing circuit, and a control device in said control circuit responsive to said current supplying means and arranged to produce said predetermined condition or said control circuit in response to a single alternationof'the current in said energizing circuit above a predetermined level. V

3. In combination with an X-ray tube and energizing circuit therefor, a control circuit, means responsive to a predetermined condition of said control circuit for disconnecting said energizing circuit, means supplying current to said control circuit varying inaccordance with current variations in said energizing circuit, settable means in said control circuit'having various positions for varying an electrical characteristic of said control circuit, and a control device in said control circuit responsive to said current supplying means and to said settable means and arranged to produce said predetermined condition of said control circuit in response to current in said energizing circuit above a level predetermined by said set table means.

4. In combination with an X-ray tube and energizing circuit therefor, a control circuit, means energized by a flow of electric current in said control circuit for disconnecting said energizing circuit, means for supplying current to said con.- trol circuit varying in accordance with current variations in said energizing circuit, a device normally blocking current flow in said control circuit but adapted tobe overcome and rendered conducting by. voltageabove a predetermined level,

whereby when said current supplied to said con- 5. In combination. with an X-ray tube anden- I ergizing circuit therefor, a control circuit, means energized by a flowpf electric current in said con- :,6..:In-7combination ergizing :circuitf therefor, a 'control lcircuit',rmeans,,;

damn-'29s I nor circuit' foi disconnecting saidienergizingrcircuits means'ffior' supplying current t to said control circuit varying in accordanceiw'th current variations in said eneigizingwczircnit thermionic-vac- --:tube.:depending uponrtherelative voltage supplied to said elementscnieans supplying: currentrtolone 10f aidnontrolaelements ."from saidscurrentasum -1o- =trol-qcircuit varying =-in accordance withcurrent nvariations in-said energizingcircuit; a thermionic vacuum-' tube positioned 'in said- "control circuit lkplyi meanswanwmeans: supplyingrairfixed ivolta'ge tcurrent tosth'e'otherronsaidtube:controlielements, a whereby whenz-said current supplied -'-to asa'id one "control element nvercomes the? fixedvvoltage sup- -pliedz;to '.said?other control element; said tubeiand,

itlrereforeisaid control circuit lbecomesrconducting i; and causes a Sdisponnectioni' ofi saidrenergizing: cirh ianixeray tube"and -enenergized byra flowaof; electric':currentrin saidcon- -:trol:circuit .iior disconnecting; saidcenergizingzacir- 'rcuit; means Piorrsupplyingscurrent 'toi'swi'ds control :cir'cuitzvaryingi inr.accordancerwithacurrent .variaand vmeanss supplying'l'a; fixed voltagezcurrent .to

- .said:gr.id ofr-a valve biasing said tubdnonconduct Jing-Tfitia, safezzpredeterminedivalue 'ofrcurrent sup- .:-plied:torsaidtplatefiwherebyz when: currentcabove --.r'said:;predetermined :va'lu 'eiisrsuppliedi tozsajdu plate tpliedtorsaid control circuit raises-sarawoidee abo vees -predetermined level said device -pen ndopera-tes saidflrstnarned'means. V

QE In combination w'itlranX ray"tube aridenergizing-icircuit therefor; a control' circuit, means control circuit ior-' disconnecting said "energizing circuit, means for "supplying *current to'saidmonand-r controllingrcurrntllow therein and having two tu-be icontrol -'elements, the conductivity of esaid tube depeirding -'upon the relative voltage supplied to said elements; ineans supplying currentlto one or saidlcontro'l elementsfrom-said'current supply =meansg said last "namedcurrentsupplying-'- means including a 5 plurality of: -flow-'conof said-plurality'o'f flow controlling-meansy'and means supplying a fixed voltagecurrenttof-thel other of 'saidtube control elements, whereby-when ssaid:current-supplied tosaid one controhelement overcomes the fixed voltage supplied-to said other control element, said tube and thereforesai'd control "circuit becQmesnon'ducting and causes disconnectiomof saidener'glzing'circuit.

j 3:10, In'combinatiomwith anX-ray tubeand' en- 'ergizing circuit therefon-a control";circuitymeans energized by a flow, o'f-electric current in said con said" tubez1and:thereforeisaidircontrokcircuitibeg mu djsconnegbing aid energizing *circomes conductingandjnauses disconnectiomofsaid r.energizingmircuit; i

' 7; In),combinationnwtithfian :Xnay tubevandxan a energizing 1 circuitertherefor nincludingira' :transi former 'having atrlow :tension primarycand: aihigh q tension secondary; a2control:ci'rcuit,:means:'enervgizedjby. arflowof-zelectricz current in saidrcon-trlol acircuit LfOI' disconnecting saidrenergizingxcircuit, means 1 for supplyingtdirecticurrent to saidgcon trol :circuit including: aitrans-former, having-a; pri-z rrnaryin parallel circuit-withsaid.firstnamedprimary ,andasecondary, a *rectifienein circuitiwith -said lastnamed secondary, a thermionic-vacuum tube positioned :innsaidicontrol: rcircuitaand econtrolling current? flow. thereinrsaid .tube havingra control grid-ands; plate;means-supplyingcurrent "to said plate: from said: rectifier; andrmeans sup- Y, plying; a .fixedfivoltagewcurrenta to said :grid :ofwa

value biasing :said': tube nonconducting'giatiiae safe epredetermined valua'iofcurrent asupplied'zto sa-id 1 plate', "whereby when current above said predetermined value is supplied to said plate said tube and therefore said control circuit becomes conducting and causes disconnection of said energiz ing circuit. 1

'8. In combination-With an X-ray tube and energizing circuit therefor, a control circuit, means energized by a flow of electric current in said control circuit for disconnecting said energizing circuit, means for supplying current to said control circuit varying in accordance with current variations in said energizing circuit, a device normally blocking current flow in said control circuit but adapted to be overcome and rendered conducting by voltage above a predetermined level, a, plurality of current flow controlling mean in said control circuit and in circuit .with said device, means for selecting the tube load for. said X-ray tube, and means for concurrently setting said predetermined level by selecting the proper flow concuitgmeans for supplying current? to said control "circuit varying in accordance with currentivariations in 'saidenergizing circuit; ai'thermionic" vacuum tube positioned in said control circuitrand ,lw controHing "current flow therein-ysaid tubehaving a control grid' and a plate, means; supplyin cur- "rentto said pla-tefrom said current supp-1y means, 1 saidlast namednurrenti'sllpplying means including a plurality of fiowc'ontrolling means in. said *control circuit andfin circuit with'sa'id plate, and one"control-'meansfor selecting; the tube load'for said'X-ray'tu-be and for selectin acorrespon'ding one; of ,said plurality 'of flow controlling. means,

ing at ;a',:safe predetermined value of currezitsunf plied to jsaid' plateflwhereby when current above "said predetermined value is supp1ied ..to. said plate,

said .tube, and therefore ;'said control. ,circuit'gbecomes conducting and 'causes. disconnection .of

0 tension secondary, a control circuit, means ener-,

gized by a flow of electric current in said control circuit for disconnectingsaid energizing circuit, means for supplying direct current to said control circuit including a transformer having a primary in parallel circuit with said first named primary and'a secondary, a rectifier'in circuit with said last named secondarlna thermionic vacuum tube positioned in said control circuit and controlling current flow therein, said tube having a control grid and a Plate, means. supplying current to said I cuit with said plate, and one control means for trolling means, whereby e Said-current supselecting the tube load for said X-ray tube and mits sai'd flowor current in said control circuit for selecting a corresponding one of, said plurality of snow controlling means, and means supplying, a

fined voltage current to said grid of a value biasing c said tube nonconducting'at a safe predetermined value ofcurrent suppliedto said plate, whereby when current above said predetermined value is supplied to said plate, said tube and therefore said disconnectionof said energizing circuit.

.12. In combination with an X-ray tubeand.

I energizing circuit therefor, a control circuit, meanscontrolled by one conductive state of said control circuit for disconnecting said energizing circuit, means for supplying current to said control circuit varying in accordance with current variations in said energizing circuit, a device in said control circuit normally maintaining said control circuit in the'other conductive-state from that first mentioned, and said device changing said control circuit to said first mentionedone conductive state responsive to current in said control circuit corresponding to current in said ener- 1 gizing circuit above a predetermined level 13. In combination with an X-ray tube and energizing circuit therefor, a control circuit,

means controlled by one conductive state of said controlcircuit for disconnecting'said energizing circuit, meansfor supplying current to said .control circuit varying in accordance with the load on said tube, a device ;in said control circuit normally maintaining said control circuit in the other conductive state from that one first named, said .devicechanging said control circuit to and maintaining said control circuit in said first named one conductive stateresponsive to current in said control circuit corresponding to tube load above a predetermined level, and resetting means for returning-said device to said normally maintaining condition. s I

14. In combinati-on with X-ray tube and I energizing circuit therefor, a control circuit, qrneans controlled by one'conductive state of said M control circuit for disconnecting said energizing circuit, means forvsupplying: current to said control circuit varying in accordance with the load-on said tube, a space discharge device in said control circuit having two control elements controlling the conductive state of saidcontrol circuit, means 1 providing a biasing current forone of saidelements such that said device normally maintains said control circuit in the other conductive state 'from that one first named, means supplying cur- "rent to the other of said elements varying as the current varies in said control circuit, and the relation between the currents supplied tosaid elements being such that said device changes to said control circuit becomes conducting and causes first named one {conductive state responsive to current in saidcontrol circuit corresponding to tube load-above a-predetermined level.

15. In combination with an X-ray tube and energizing circuit therefor, a control circuit, means energized by flow of electric current in said control circuit for disconnecting said'energizing circuit, means for supplying-current to said control circuit varyin'g in accordance with the'load on said ,tube,xa space discharge device havin two control'elements controlling the conductive state of said'control circuit, means providing abiasin u currentfor oneof said elements suchthat said device is normally'non-conducting, means supplying current to the other of said elements varying as the current varies in said control'circuit, the'relationfloetween the currents supplied'to said elements being such that said device changes to a conductingstatej responsive to current in said controlEcircuit corresponding to tube load above a predetermined level; and the current supplied to one of said control elements of said space .discharge device being' rectified, whereby said device upon becoming conducting tends to remain in that stateJ Y 16. The combination of claim 15 includinga plurality of separate current flow controllin means in saidcontrol' circuit, and selector means movable from one to the other of said last named separate-flowcontrolling means and breaking said control circuit when in intermediate position between them, whereby When said'spacedischarge device is in conducting state movementof said selector means to an intermediate position breaks said controlcircuit permitting said device to return to its normal non-conducting state.

17. In combination with an X ray tube and 1 energizing circuit therefor, a control circuit, means controlled by one conductive state of said control circuit for disconnecting said energizing circuit, means for supplying current to said con trol circuit Varying in accordance with the load on said tube, "a' plurality of flow controlling means adapted to be selectively connected in said control circuit, a devicein said control circuit controlling the conductive state thereof and normally maintaining said control circuit in the other conductive'state from that one'first named, said device changing said control circuit to and maintaining said control circuit in said first named one conductive "state responsive to current in said control circuit above a predetermined level,- and one control means for selecting the tube load for said X-ray tube and for selecting a corresponding one of said plurality'offiow controlling means. t JACK'BALL. 

